1. Field of the Invention
The invention pertains to the field of variable cam timing. More particularly, the invention pertains to controlling the phaser to vary the timing of the cam using the spool valve.
2. Description of Related Art
U.S. Pat. No. 5,002,023 shows a single check valve in a spool valve which is present in the rotor.
U.S. Pat. No. 5,172,659 shows dual check valves in the rotor between the chambers and the spool valve. A single check valve is present in the spool itself.
U.S. 2003/0070713A1 discloses a valve arrangement having a valve member in a cylindrical sleeve, where the sleeve has several bores in which hydraulic medium can flow through. A rectangular strip-shaped member made of springs steel surrounds a bore of the sleeve, sealing the bore. The strip-shaped member expands when the hydraulic pressure reaches a certain pressure.
JP11013430A discloses a selector mechanism in the middle of an oil pressure passage in the camshaft. Two check valves are present in the selector mechanism. Each check valve has a ball, received by a seat in a body that is slanted. A slidable selecting piston slides back and forth between the two check valves and first with the slant present on the check valve body, allowing fluid to move through only one check valve at a time to a hydraulic chamber.
The “Pictorial Handbook of Technical Devices” by Grafstein & Schwarz on pages 376–377 shows a shuttle valve, identified by “d”. As shown in “d”, the valve has two inlets and one outlet. Two check valves block low pressure from the sides of the valve. Shuttle valves are commonly used to isolate a normal operating system from an alternate/emergency system. So, one of the inlets is to the normal operating system and the other is for the emergency system. The shuttle slides and blocks the emergency inlet during normal operation by normal system pressure. The emergency inlet remains blocked until the emergency system is activated. At this time, the shuttle moves, blocking the normal system inlet, allowing free flow from the emergency inlet to the outlet.
The 2nd edition of the “Automotive Handbook” by Bosch, pages 634–636 discloses a spool valve comprising a valve body, a load, metering notches, a spool a, a check valve, and a return spring. The check valve is located in the body of the spool and acts as a one way flow device for the inlet line of the spool valve. On pages 636 & 637, a hydraulically unlockable double check valve is shown. The valve comprises a poppet valve, an unlockable piston and two check valves. The check valve may be opened mechanically, hydraulically, or electrically.